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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* This file incorporates work covered by the following license notice:
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed
* with this work for additional information regarding copyright
* ownership. The ASF licenses this file to you under the Apache
* License, Version 2.0 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.apache.org/licenses/LICENSE-2.0 .
*/
#ifndef INCLUDED_STOC_SOURCE_SECURITY_LRU_CACHE_H
#define INCLUDED_STOC_SOURCE_SECURITY_LRU_CACHE_H
#include <memory>
#include <unordered_map>
// __CACHE_DIAGNOSE works only for OUString keys
#ifdef __CACHE_DIAGNOSE
#include <osl/diagnose.h>
#include <rtl/ustrbuf.hxx>
#include <rtl/ustring.hxx>
#include <rtl/string.hxx>
#include <sal/log.hxx>
#endif
namespace stoc_sec
{
/** Implementation of a least recently used (lru) cache.
*/
template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
class lru_cache
{
struct Entry
{
t_key m_key;
t_val m_val;
Entry * m_pred;
Entry * m_succ;
};
typedef std::unordered_map< t_key, Entry *, t_hashKey, t_equalKey > t_key2element;
t_key2element m_key2element;
::std::size_t m_size;
std::unique_ptr<Entry[]> m_block;
mutable Entry * m_head;
mutable Entry * m_tail;
inline void toFront( Entry * entry ) const;
public:
/** Default Ctor. Does not cache.
*/
inline lru_cache();
/** Retrieves a pointer to value in cache. Returns 0, if none was found.
@param key a key
@return pointer to value or 0
*/
inline t_val const * lookup( t_key const & key ) const;
/** Sets a value to be cached for given key.
@param key a key
@param val a value
*/
inline void set( t_key const & key, t_val const & val );
/** Sets the number of elements to be cached. This will clear previous entries.
@param cacheSize number of elements to be cached
*/
inline void setSize( ::std::size_t size );
};
template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::setSize(
::std::size_t size )
{
m_key2element.clear();
m_block.reset();
m_size = size;
if (0 < m_size)
{
m_block.reset( new Entry[ m_size ] );
m_head = m_block.get();
m_tail = m_block.get() + m_size -1;
for ( ::std::size_t nPos = m_size; nPos--; )
{
m_block[ nPos ].m_pred = m_block.get() + nPos -1;
m_block[ nPos ].m_succ = m_block.get() + nPos +1;
}
}
}
template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
inline lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lru_cache()
: m_size( 0 )
, m_block( nullptr )
, m_head( nullptr )
, m_tail( nullptr )
{
}
template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::toFront(
Entry * entry ) const
{
if (entry != m_head)
{
// cut out element
if (entry == m_tail)
{
m_tail = entry->m_pred;
}
else
{
entry->m_succ->m_pred = entry->m_pred;
entry->m_pred->m_succ = entry->m_succ;
}
// push to front
m_head->m_pred = entry;
entry->m_succ = m_head;
m_head = entry;
}
}
template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
inline t_val const * lru_cache< t_key, t_val, t_hashKey, t_equalKey >::lookup(
t_key const & key ) const
{
if (0 < m_size)
{
typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
if (iFind != m_key2element.end())
{
Entry * entry = iFind->second;
toFront( entry );
#ifdef __CACHE_DIAGNOSE
OUStringBuffer buf( 48 );
buf.appendAscii( "> retrieved element \"" );
buf.append( entry->m_key );
buf.appendAscii( "\" from cache" );
SAL_INFO("stoc", buf.makeStringAndClear() );
#endif
return &entry->m_val;
}
}
return nullptr;
}
template< typename t_key, typename t_val, typename t_hashKey, typename t_equalKey >
inline void lru_cache< t_key, t_val, t_hashKey, t_equalKey >::set(
t_key const & key, t_val const & val )
{
if (0 < m_size)
{
typename t_key2element::const_iterator const iFind( m_key2element.find( key ) );
Entry * entry;
if (iFind == m_key2element.end())
{
entry = m_tail; // erase last element
#ifdef __CACHE_DIAGNOSE
if (entry->m_key.getLength())
{
OUStringBuffer buf( 48 );
buf.appendAscii( "> kicking element \"" );
buf.append( entry->m_key );
buf.appendAscii( "\" from cache" );
SAL_INFO("stoc", buf.makeStringAndClear() );
}
#endif
m_key2element.erase( entry->m_key );
entry->m_key = key;
::std::pair< typename t_key2element::iterator, bool > insertion(
m_key2element.emplace( key, entry ) );
OSL_ENSURE( insertion.second, "### inserting new cache entry failed?!" );
}
else
{
entry = iFind->second;
#ifdef __CACHE_DIAGNOSE
OUStringBuffer buf( 48 );
buf.appendAscii( "> replacing element \"" );
buf.append( entry->m_key );
buf.appendAscii( "\" in cache" );
SAL_INFO("stoc", buf.makeStringAndClear() );
#endif
}
entry->m_val = val;
toFront( entry );
}
}
}
#endif
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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